This invention relates to circuit controls, and particularly to circuit controllers of the kind which initiate a controlled action in response to a physical condition such as illumination, temperature, humidity, barometric pressure, etc., and the control action is terminated on the basis of time.
A typical application for such a device occurs in regulation of outdoor lighting equipment that is intended to illuminate an area during its normally used evening or nighttime hours. One available type of device is interposed between the current carrying lines and a load. It is composed of a photosensitive element that causes a relay to permit actuation of the lights at sunset in response to the diminishing ambient sunlight. At sunrise the photocell responds to the increasing ambient light and causes the relay to cut off power to the lighting equipment. Such devices are satisfactory but tend to waste substantial amounts of current during the early morning hours when the illuminated area is unused.
Other types of devices for actuating loads in response to physical conditions are illustrated in U.S. Pat. Nos. 3,091,723 and 3,350,581. One of these systems is capable of solving the problem of energy waste by energizing the light only for a predetermined period of time after sunset. However, such a system fails to consider changes in the times of sunrise and sunset throughout the year. If, during the summer, the timing mechanism used is set to turn off the lights 5 hours after a 9 P.M. summer sunset, the same timing mechanism would extinguish the light 5 hours after a 5 P.M. winter sunset, namely at 10 P.M. Such a system is not completely satisfactory if the illuminated facilities are to be used until 2 A.M. On the other hand, accommodating the timing mechanism to a 5 P.M. winter sunset, so that it would extinguish the lights 9 hours later at the desired time of 2 A.M., would result in illumination throughout the night and after sunrise during the summer months.
An object of this invention is to improve conditioninitiated load-controlling systems.
Another object of the invention is to alleviate the aforementioned difficulties.
Another object of the invention is to provide means which can be added to existing means for controlling such loads.